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skew angle on rebate (rabbet) planes

I'm thinking of making a pair of skew rebate planes for the woodie build-off. Looking around on the web I find the skew angles vastly different on these planes. For example Terry Gordon's is skewed at 4*, while the Veritas skew-block is 15* and the Veritas Skew Rabbet is skewed at 30*. Quite a difference. I'm wondering, in terms of usage, what difference these angles make. Thanks.
-Howard

The difference between them? I don't know; I have the 18* Lie Nielsen skew block (w/ fence and nicker).

In addition to the skew angle lowering the effective cutting angle, when cutting rabbets it also tens to pull the plane into the corner of the rabbet, making it easier to keep the rabbet corner square.

One can never have too many planes and chisels... or so I'm learning!!

It's like walking up a hill at an angle instead of straight up the hill. Much less steep right? There is less rise (vertical distance) to your run (movement forward). The greater you direct your movement across the slope of the hill, the less distance you progress up the hill with each step forward you take - (e.g. the angle at which you are traveling upward is less steep). Similarly, the wood isn't hitting the blade bevel dead on, rather its going partially across the bevel as it engages so the rise to run is less steep. I bet Dave W can explain it better - hes a mathematician. I'm just a former middle school math teacher.

It just kind of is. Take a block and cut it off at a rough angle. Measure a plane blade with a protractor against your bench top, then skew the plane and measure it again. Or use a block cut off at an angle.

The way it had always been explained to me was to think about walking up a hill. If you go straight up, it's steeper than if you climb up at an angle to the slope. . .

EDIT: That's what I get for not hitting refresh before reply - Chris beat me to it!

The only easy way I can explain it is to take an iron and draw a line straight back while it's 90 degrees to a cut (draw the line up the bevel, but not onto the iron).

Then turn the iron 45 degrees and draw a line straight back in the direction the cut would be if you were cutting with the iron skewed 45 degrees.

The second line will be longer, but will reach no higher in height. The only way for that to be the case is for the effective angle to be lower.

The extreme case, that may make it easier for someone to understand if they still don't see it after that is to turn the iron just shy of 90 degrees. It takes nearly the width of the iron to rise to a height that is less than the iron's thickness. That's really shallow.

I'm thinking of making a pair of skew rebate planes for the woodie build-off. Looking around on the web I find the skew angles vastly different on these planes. For example Terry Gordon's is skewed at 4*, while the Veritas skew-block is 15* and the Veritas Skew Rabbet is skewed at 30*. Quite a difference. I'm wondering, in terms of usage, what difference these angles make. Thanks.
-Howard

Like Chuck said, skew angle impacts the cutting geometry. It also effects how much the plane will tend to drift in the cut, which can be a problem if you're trying to start the rabbet free-hand without a batten. If you're making wooden planes one big issue you need to consider is what angle you have your floats skewed at. You're dealing with a compound angle and the skew of the float will result in a different skew angle for the different bed angles. I'm really never working with or considering the actual skew angle of the plane, I'm trying to stay true to the skew angle of the floats. Keeping the mortise with the proper size parallelogram shape is something I find pretty challenging. I have 1/8" and 3/16" thick pairs of left and right hand floats made with several different angles but can't tell you what exact skew angle plane they'll make at the different bed angles. I'd sit and do the math but it's not something I use. Maybe I can remember to measure the skew angle of some of the planes we have and try to remember which floats were used to make them.

On edit. The breast and bed or bed and wear on skewed planes are actually cut at different angles because they're at different angles to the sole. I cut the bed to the float skew angle and work my way into fitting the wedge at its front edge. I don't have floats made to all the angles for the front of the mortise. If I did, at some point I'd be working with the wrong float for what I'm working on.

Last edited by Larry Williams; 02-25-2012 at 12:14 AM.
Reason: add a little more

Larry, I'm curious, I read in Whelan's book, which my brother got me as a gift, that you can use triangular saw type files as floats. Anneal them, and grind/sand it smooth, and cut teeth into it. Have you tried this, or do you find it doesn't provide enough clearance still? It seems like it might work okay, though.

On another note (but which also might be of interest to Howard), what's your preferred method of cutting the conical escapement, Larry? Do you use a multiple blade pipe reamer, or do you step drill it and use a rasp/gouge?

The more skew, the smoother the cut and the smaller the area cut. Think of it as leverage. A larger skew means more blade passes but less wood is cut.

When working rough wood with a straight plane, I tend to angle it much more that when I am working easy wood. The angle that works best for you on the worst wood you cut might be a good angle for the skew. It is nice to have at least enough cutting width remaining after the skew, to cut the entire face of the rebate you normally make.

So, while you can copy another planes skew, you can also make a skew that suits your style of woodworking.

I am thinking about making a pair of skew planes that don't reach into the corner. That way I can use them on a shooting board. I am not sure how the lift movement that a skew can make will work out on a shooting board, but I could always take down the side and turn them into skews for rebates if the idea does not work out.

That seems to be the best method, but that might also tend to lift the wood being planed. I will not know for sure until I do it. With a right and left plane, I can try both, and if it fails, I end up with two of the largest skew rabbets anyone has seen!